This invention relates to the production of useful hydrocarbon from hydrocarbon feed. More particularly, the invention relates to a process and apparatus for cracking hydrocarbon feed by the use of heated solids.
Conversion of hydrocarbon feed to useful products such as fuel, olefins, etc., is now well known. Many processes have been developed to crack crude hydrocarbon to produce useful products. Among the conventional processes are pyrolysis cracking and catalytic cracking processes. In recent years, both pyrolysis cracking and catalytic cracking have implemented systems in which particulate solids are used as the heat source to promote cracking of the hydrocarbon feed.
In effect, particulate solids, either inert or catalytic, are heated and introduced into a cracking zone with hydrocarbon feed. The hydrocarbon feed is cracked in the cracking zone and the heated particulate solids lose heat and are fouled or contaminated with the tars and other heavy components of the hydrocarbon feed. Thereafter, typically the contaminated solids are regenerated for re-use in cracking hydrocarbon feed. Regeneration entails burning the contaminants from the solids and elevating the temperature of the particulate solids to the level necessary to crack the hydrocarbon feed.
Each cracking process in which particulate solids are used requires delivery and separation means to both engage the solids with the hydrocarbon feed and to separate the solids from the cracked product gases produced in the process.
Recently, a process and an apparatus have been developed by Stone and Webster Engineering Corporation that efficiently and effectively separates particulate solids from the cracked gases leaving a cracking reactor. U.S. Pat. No. 4,433,984 and others describe the separation process and-apparatus that has minimized the contact time in separation of the particulate solids and cracked gases while achieving separation to a level desired for terminating cracking reactions.
Similarly, Stone and Webster Engineering Corporation has developed a process and an apparatus for delivering particulate solids to a service such as a fluidized bed furnace which eliminates moving mechanical parts and thereby enhances the function and reliability of the delivery system. The process and apparatus are described in U.S. Pat. No. 4,459,071. Essentially, the system relies on regulated pressure differentials to promote or interrupt the flow of solids to a location.
In addition, Stone and Webster Engineering Corporation has developed a process and apparatus for injecting hydrocarbon feed into a moving path of hot particulate solids to achieve rapid and complete cracking of the hydrocarbon feed. U.S. Pat. No. 4,338,187 and others describe a hydrocarbon feed and hot particulate solids feed system that achieves rapid mixing of the feed and solids and the desired attendant rapid cracking.
It is an object of the present invention to provide a process and apparatus that will facilitate complete and rapid cracking of hydrocarbon feed followed by rapid separation of the cracked gases from the particulate solids.
It is also an object of the present invention to provide a process and apparatus for rapidly separating cracked effluent from particulate solids and terminating the reactions in the cracked effluent by immediate quench.
It is another object of the present invention to provide a process and apparatus that affords controlled positive and reliable delivery of particulate solids to service locations such as the cracking reactor.
It is a further object of the present invention to provide a process and apparatus for effectively and efficiently regenerating particulate solids.
Another object of the present invention is the provision of a process and apparatus that achieves essentially complete separation of flue gases from the regenerated particulate solids.
It is also an object of the present invention to provide a process and apparatus that will enable hydrocarbon feed to be cracked with heat carried by regenerated particulate solids; and thereafter, facilitate separation of the particulate solids from the cracked effluent; and regenerate the solids for re-use as the heat source for a cracking reactor.
Thus, there is provided an apparatus comprising a reactor system, a regeneration assembly and a solids delivery assembly. The reactor system comprises of an essentially rectangular mixing zone; a tubular reaction vessel connecting the mixing zone to a separation means; a separation means to rapidly separate the cracked effluent from the particulate solids; cracked effluent quench apparatus immediately downstream of the separation means; and a final separation means. The regeneration assembly includes a stripper, an entrained bed heater and a flue gas-regenerated solids separation vessel. The solids delivery system includes a standpipe and an upper hopper.
The process proceeds by delivering a curtain of hot particulate solids through discrete essentially rectangular inlets to the mixing zone of the reactor at a controlled rate and simultaneously contacting the hydrocarbon feed with the solids curtain. After a short residence time in the reactor, the cracked effluent is separated from the hot solids, quenched and sent to conventional recovery equipment for product collection.
The particulate solids discharged from the reactor are at a reduced temperature from the temperature at which the solids entered the reactor and have become fouled with contaminants such as tar and coke from the hydrocarbon feed. The particulate solids are first stripped of some of the impurities and then heated in the entrained bed heater by combusting fuel and air with the coke contaminants on the solids.
The combustion gases generated in the entrained bed heater and regenerated solids travel upwardly to the regenerated solids separation vessel wherein the combustion gases are separated from the regenerated solids and exhausted as flue gases.
The regenerated particulate solids are collected in a slumped bed above the standpipe which terminates in a reactor hopper that is in direct communication with the rectangular solids entry to the reactor.